CP23  Hyperkalemia

 

The Heart and Hyperkalemia

               Most of the body’s potassium is located intracellularly.  Onl a small fraction (=2%) is  found in the extracellular compartment.  As serum potassium concentration increases, a decreased ratio of intracellular to exrtracellular K+concentration occurs, and results in a decreased resting cell membrane potential.  Increased serum Na+ and Ca+ concentrations limit depolarization of the cell membrane.  In addition, there is shortening of the action potential duration from increased membrane permeability to K+.  Mild hyperkalemia (6.0mEQ/L), with normal renal function generally needs no treatment.  Moderate hyperkalemia (6.0-7.0mEq/L), with normal renal function generally resolves with time and no therapy.  Severe hyperkalemia (7.0mEq/L), especially with EKG manifestations, requires immediate therapy.  Renal excretion accounts for total maintenance of potassium balance.

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Causes of Hyperkalemia

-Cardioplegia solutions

-Transfusion of overaged banked blood

-Renal dysfunction from any cause

-K from cell hemolysis

-Acidosis

-K sparing diuretics ( Spironalactone, Triamterene, Amiloride)

-Ace inhibitors

-Digitalis in high doses

-KCL supplementation

-Drugs causing tumor lysis

-Low insulin production (DM)

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Treatment of Hyperkalemia

1. If you get a lab value back that is questionable, be sure to send another sample for a repeat value. In the meantime, alert anesthesia to the possibility of true hyperkalemia, and the necessity for treatment of it.
2. Stop all infusions containing K+ (cardioplegic solution, priming solutions, IVs).
3. Increase the elimination of K+ from the extracellular fluid:
4. Infuse Dextrose and Insulin:

1-2g glucose/kg in children

0.3U R insulin/glucose in children

50g glucose and 15U R insulin in adults

1. NaHc03:

1-2mEq/kg children

45mEq adults

1. Calcium:

20mg/kg calcium gluconate over 5 min in children

500-1000mg of calcium chloride in adults

1. Increase dieresis
2. Hemoconcentration on CPB: Hemoconcentrate off as much as pump volume as possible, adding normal saline (for injection) as needed for volume replacement.  Recheck K+ and electrolye levels often.
3. Hemodialysis for persistent hyperkalemia.
4. Emergency cardiac pacing if severe hyperkalemia is causing arrhythmia’s.
5. If you are aware preoperatively that your patient is hperkalemic, during CPB you can scavenge the initial flush of cardioplegia to the cell saver.

 

*Note: All of the above listed procedures are contingent upon approval with both the surgeon and anesthesia.

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HOW TREATMENT OF HYPERKALEMIA IS ACHIEVED

NaHcO3:  Correction of acidosis by diminishing the extracellular hydrogen burden and transfer of K+ intracellularly, provides intracellular binding sites for K+ in the form of potassium carbonate, buffers dextrose; corrects acidosis from shift of H+ from intracellular to extracellular.

Hypertonic saline: Correct hyponatremia; counteracts cardiotoxicity; expands extracellular compartment and dilutes K+.

Glucose and insulin: Directly promotes the movement of K+ from extracellular to intracellular compartments.

Calcium: Activates receptor sites of potassium pumps on cell membranes; replaces serum Ca, which is driven intracellularly by administration of insulin.